Lecture Notes on December 2021 Severe Weather Events

Introduction

• December often associated with holiday celebrations.
• 2021 saw severe weather events, notably a tornado outbreak on December 10-11.
• EF4 wedge tornado struck Mayfield, Kentucky.
• Mayfield tornado one of the costliest, deadliest since Joplin 2011.
• December 15th brought another severe event: a derecho and tornado outbreak.
  • Largest tornado outbreak in December.
  • Derecho one of the strongest in US history with hurricane-force winds.

Key Weather Events of December 2021

December 15th Derecho

• Final major severe weather event of 2021.
• Multiple hazards: fire weather, strong winds, winter storm, tornado threat, and derecho.
• Linear storm mode with strong wind shear, low-pressure system, and moisture needed for derecho.

Explanation of Derecho

• Defined by National Weather Service as a widespread, long-lived windstorm.
• Requires line of wind damage over 240 miles with gusts of at least 58 mph.
• Conditions: linear storm mode, adequate CAPE, strong wind shear, low-pressure system, moisture.

Analysis by Meteorologist Nick Stewart

• Fire weather conditions in central plains, extreme risk for Kansas, Oklahoma, and Texas.
• Strong winds due to deepening low-pressure system and tight pressure gradient.
• Winter storm threat and rapid transition from severe to winter weather.
• Severe weather: high instability (CAPE) and wind shear.
• Tornado threat: strong low-level winds and helicity.

Detailed Event Timeline

• Strong winds and severe weather warnings across central US.
• Tornado watch issued for Kansas, Missouri, Iowa, Minnesota.
• Severe thunderstorms and tornadoes in Iowa.
• Derecho with hurricane-force winds causing significant damage and power outages.

Aftermath and Impact

• Significant power outages and damage reported.
• 120 tornadoes confirmed, 33 EF2 strength.
• Derecho lasted 8 hours, with widespread wind damage.
• 5 fatalities and $1.8 billion in damages.
• Derecho and tornado outbreak significant for December, research-worthy.

Observations and Remarks

• Success in communication and warning efforts by meteorologists and emergency services.
• December 15th event researched for its unusual circumstances, akin to summer severe weather.
• Meteorological community performed well in forecasting and managing communications.

Conclusion

• December 15th event a historic and research-worthy severe weather event.
• High cooperation in meteorological community in warning the public.
• Continues to be a significant topic in severe weather research.